1. Field of the Invention
The present invention relates to a rack-and-pinion steering apparatus having a so-called drop-in structure.
2. Description of Related Art
In a rack-and-pinion hydraulic power steering apparatus having a drop-in structure, for example, a valve housing for accommodating a hydraulic control valve incorporates the hydraulic control valve and a pinion shaft serving as an output shaft, to form a sub-assembly. The pinion shaft in the sub-assembly is then inserted into (dropped into) a pinion housing. The valve housing and the pinion housing are then connected to each other, to complete assembling work.
An outer ring in a bearing for supporting the pinion shaft is held along the axis of the pinion shaft between receiving sections respectively provided in the valve housing and the pinion housing. When the distance between the receiving sections is larger than the size in the axial direction of the outer ring, a clearance in the axial direction occurs between the receiving section and corresponding end surface of the outer ring. As a result, backlash may be produced along the axis of the pinion shaft against both the housings to produce abnormal sound at the time of steering. Further, response to production of a steering assist force is degraded in the case of steering.
Therefore, it is proposed that an elastic member such as a spring washer or rubber is interposed between the receiving section in the pinion housing and the corresponding end surface of the outer ring (see Japanese Unexamined Patent Publication No. 9-66850 (1997) and Japanese Unexamined Patent Publication No. 2002-145092, for example).
On the other hand, in order to apply a pre-load to the bearing for supporting the pinion shaft, it is proposed that an elastic member such as a belleville spring for urging the bearing in the axial direction is used (see, Japanese Unexamined Patent Publication No. 10-175559 (1998), for example).
However, the elastic member such as the spring washer or the rubber may be easily subjected to degradation such as fatigue due to changes with time. When the elastic member is degraded, a clearance in the axial direction may occur between the outer ring in the bearing and the corresponding receiving section.
The above-mentioned problem that abnormal sound is produced exists in not only the hydraulic power steering apparatus but also a manual power steering apparatus.
An object of the present invention is to provide a steering apparatus that can prevent abnormal sound from being produced over a long time period.